Anharmonicity of zone-centre optical phonons: Raman spectra of the isomorphous alpha-quartz, berlinite and gallium phosphate in the temperature range8-300 K

The temperature dependence of the optical-phonon wavenumbers and bandwidths in the isomorphous alpha-quartz, berlinite (AlPO4) and gallium phosphate ( GaPO4) was investigated by Raman scattering experiments in the temperature range 8-300 K, Combining these data with those from high-pressure Raman sca ttering experiments (up to 20 GPa), we estimated the implicit (thermal volu me expansion) and explicit (pure self-anharmonic) temperature contribution to the temperature wavenumber shifts observed in isobaric experiments. In t he framework of the Gruneisen approximation, the mode-Gruneisen parameters of the A(1) modes in GaPO4 are given. As expected, these results are simila r to those previously reported for quartz and berlinite, In the temperature range 8-300 K, which is less than the alpha-beta temperature of transition (Talpha-->beta approximate to 850 K) of quartz and berlinite, the phonon p opulation decay processes appear to be the main cause of phonon damping in the three materials. Copyright (C) 2000 John Wiley & Sons, Ltd.